Control system



219370 J. ALEXANDER, m CONTROL SYSTEM Filed Janv 16, 1935 lmventor": James R. Alexander Jr".

Hi 5 jkbtor ney Patented Dec. 21, 1937 James 8.. Alexander, Jr., Lansdowne, Pm, assignor to General Electric Company, a corporation of New York Application January 16,1935, Serial No. 2,016

11 Claims.

This invention relates to control systems, and it has for an object the provision of a simple, reliable and improved system of this character. In one of its aspects, this invention relates to 5 systems for controlling an operating characteristic or condition of apparatus, the operations of which are subject to hunting action, such for example, as rotary kilns and the like, and one of the specific objects of the invention is the pro- 30 vision of means for eliminating this hunting action.

Incarrying the invention into effect in one form thereof, means controlled by suitable electric valve apparatus are provided for varying or controlling an operating condition of the device which is to be controlled, and means are provided for producing a control voltage varying with the controlled condition for actuating the electric valve apparatus in response to variation 110 in the controlled condition from a predetermined value, together with means actuated by the operating condition varying means for producing a voltage opposing the control voltage for controlling the electric valve apparatus in such a manner as to eliminate the hunting action.

In illustrating the invention in one form thereof, it is shown as embodied in a system for controlling the speed of a rotary cement kiln in suitable relation with the temperature of the kiln. In the present day cement manufacturing plants, inclined rotary kilns of considerable length are utilized for effecting fusion of two materials. A homogeneous mixture of these two materials is fed into the high end of a rotary kiln and during the rotation of the kiln passes through the different zones thereof to the low end or the clinkering zone. At the extremity of the clinkering zone, the cement clinker is discharged from the kiln and cooled. The union of the materials within the kiln is effected by the application of heat, which in the usual arrangement is produced by a burner projecting fuel into the kiln at the lower end thereof and discharging combustible material. It is desirable to maintain a substantially constant temperature within the kiln because any considerable variation of the temperature lowers the quality of the cement clinker and also the efficiency of the kiln. Accordingly, a specific object of this invention is the provision of means for eliminating hunting action in the operation of the kiln thereby to maintain the temperature substantially constant.

The present invention is an improvement on the invention disposed in an application of Aubrey Smith, Serial No. 757.168, Rotary kiln control arrangement, filed December 12,1934, and assigned to the assignee of the present invention. I do not herein claim anything claimed in the Smith application.

For a better and more complete understanding of the invention, reference should now be be had to the following specification and to the accompanying drawing, the single figure of which is a simple diagrammatical illustration of an embodiment of the invention.

Referring now to the drawing, an inclined rotary kiln I is rotatably supported on suitable bearings H and is rotated by suitable driving means illustrated as an electric motor l2 to the shaft of which the kiln is mechanically coupled by suitable gearing l3. Although the motor l2 may be of any suitable type, it is illustrated as a variable speed alternating current motor of the brush shifting type and is supplied from a suitable source of alternating current (not shown). The motor I2 is provided with two sets of brushes carried on rings I4 and 15 which may be adjusted, i. e. rotated relatively and oppositely to each other in either direction by means of a pilot motor I6 which is connected to the rings H and I by means of gearing as illustrated. Rotation of the pilot motor I B in one direction shifts the brushes of the motor l2 on the commutator in such directions as to increase the speed of the motor l2 and similarly rotation of the pilot motor IS in the opposite direction shifts the brushes in such directions as to decrease the speed. Fuel is supplied to the interior of the kiln at the lower end thereof by a burner H, which in turn receives fuel from a bin (not shown).

Since the quality of the material which is being processed in the kiln varies with changing temperature in the kiln, means are provided for maintaining substantially constant final temperature of the clinker in the clinkering zone of the kiln. This is accomplished by controlling the speed of the kiln in response to changes in temperature therein. These means are illustrated as a device which is responsive to the radiant energy of the clinker, such for example" as a photo-electric cell l8, an amplifying device l9 and suitable electric valve apparatus illustrated as a pair of electric valves 20 and 2| controlled by the amplifier l9, together with suitable switching means illustrated as a pair of electromagnetic contactors 22 and 23 respectively controlled by the valves 20 and M for in turn controlling the pilot motor I 6. The photo-electric cell Ill is connected in'a control circuit repre sented by conductors 24 and 25 to which circuit voltage is supplied from a suitable direct current source represented in the drawing by plus and minus signs. Thus, this control circuit is readily traced from the plus side. of the supply source by conductors 26 and 24 through photo-electric cell l8 and thence by conductor 25 through a voltage drop device illustrated as a resistor 21 to the negative side of the supply Col source. Suitable voltage dividers illustrated as a pair of variable resistances 28 and 23 connected in parallel relationship with each other and in series relationship with a variable resistance 30 to the supply source are provided for supply.

ing voltages at suitable magnitudes to the amplifying tube l9 and also to the electric valves 20 and 2|.

Although the amplifying tube l9 may be of any suitable type it is preferably of the high vacuum type and is provided with a cathode I98, a control grid I91) and a plate or anode l9d. The cathode 9a. is heated to the required degree by energy supplied from a suitable alternating current source 3| through a suitable supply transformer 32 having a plurality of secondary windings, one of which is connected to the cathode heater as shown. The cathode of the tube I8 is connected to a point of suitable potential on the variable resistance 30 and the grid I91, is connected to a point of the control circuit between the resistance 21 and the photo-electric cell I8.

The photo-electric cell I8 is focused on the hot cement clinker in the kiln so that the amount of current which flows in the photo-electric cell circuit is proportional to or dependent upon the radiant energy from the clinker which strikes the sensitive element of the photo-electric cell. Consequently, there is produced across the resistance 21 a voltage drop which varies with the temperature of the kiln, and since the grid I91; is connected to the control circuit between the resistance 21 and the photo-electric cell l8, the voltage of this grid varies in accordance with the temperature changes in the kiln. A suitable voltage drop device illustrated as a resistance 33 is connected in the cathode anode circuit of the amplifying valve I9. Thus, this circuit is readily seen to extend from the positive side of the supply source through conductor 26, milliammeter, resistance 33, anode l3d, cathode I85 and the resistance 30 to the negative side of the supply source.

Although the electric valves 20 and 2| may be of any suitable type, they are preferably of the three-electrode type into the envelopes of which a small quantity of an inert gas, such for example as mercury vapor is introduced after exhaust, thereby constituting the valves electrostatically or grid controlled arc rectifiers. The grid or input circuit of the electric valves 20 and 2| is connected to the cathode-anode circuit of the amplifying valve IS in such a manner that valves 20 and 2| are controlled in response to temperature changes in the kiln. As shown, the valves 28 and 2| are provided with cathodes 20s and 2h; respectively grids 20b and 2h, respectively, and anodes 20c and 2|c respectively. The cathodes 20a and 2|..L are heated by means of energy supplied through the supply transformer 32, to the secondary winding 32a of which the cathodes are connected as shown. Alternating voltage is supplied to the anodes 20 and 2|c through the transformer 32 to the secondary winding 32s of which the anodes are connected, through the operating coils of contactors 22 and 23 respectively and conductor 34.

As shown, the grids 20b and 2h, of the valves 20 and 2| are respectively connected to the movable contacts of the voltage dividers 28 and 29. Thus it will be seen that the input circuits of the electric valves 20 and 2| are traced from the grids 20b and 2| bto the movable contacts on the voltage dividers 28 and 29 respectively, thence through conductor 26, resistance 33, conductor 35, left hand portion of resistance 36, conductor 31,

secondary winding 32d of transformer 32 and thence by conductor 38 to the mid-point of secondary winding 32a to the cathodes 20a and 2|a respectively.

For the purpose of eliminating hunting action suitable means are provided for introducing a voltage in the grid circuit of the electric valves 2|] and 2| which is proportional to the speed of the kiln driving motor I2 and the polarity of which is opposite to the control voltage drop across the resistance 33 in the anode circuit of the amplifier tube. These means are illustrated as a small pilot generator 39 coupled to the drive shaft of the kiln driving motor l2 and having its armature connected by means of conductors 48 to opposite terminals of the resistance 36 in the grid circuit of electric valves 20 and 2|.

The pilot motor I6 is illustrated as provided with a split field winding I65 and |6s for effecting operation in opposite directions thereby to effect increases or decreases in the speed of the kiln driving motor |2 as desired. When the contactor 23 is deenergized and its contacts are closed as illustrated, the motor I8 is connected to the supply source 3| in such a direction as to shift the brushes l4, Hi to decrease the speed of the kiln driving motor l2 and when the contactor 23 is open and the contacts of the contactor 22 are closed, the motor H5 is connected to the supply source through the field winding 5a thereby to effect rotation of the pilot motor IS in the reverse direction to increase the speed of the kiln driving motor l2.

Initially the grid voltages of the electric valves 28 and 2| are adjusted by adjustment of the movable contacts of the voltage dividers 28 and 28 so that the valve 20 is non-conducting and the valve 2| is conducting when the temperature of the kiln is at the desired value. As a result, the operating coil of the contactor 22 is deenergized and the contacts are open, whilst the operating coil of the contactor 23 is energized so that its normally closed contacts are also open. Thus, the pilot motor I3 is disconnected from the supply source and is at rest and the motor |2 drives the kiln at a speed dependent upon the relative positions of its two sets of brushes.

With the above understanding of the elements and their organization in the complete system, the operation of the system itself will readily be understood from the following detailed description:

Assuming that the clinker in the clinkering zone of the kiln as viewed by the photo-electric cell I8 is at the correct temperature and that the movable contacts and the voltage dividers 28 and 29 are properly adjusted, the voltages of the grids 28s and 2|b as represented by the voltage drops across the resistances 28, 29, 33 and 36 are such that the valve 20 is non-conducting and the valve 2| is conducting. As a result the contacts of both contactors 22 and 23 are opened and there is no movement of the brush shifting motor I6. If the temperature of the kiln rises above the desired predetermined temperature, the voltage drop across the resistance 33 in the anode circuit of the amplifier tube increases and thus makes the grid voltage of both valves 20 and 2| more positive. When the voltage of the valve 20 becomes sufficiently positive, the valve 20 becomes conducting which results in energizing the operating coil of the contactor 22, causing it to close its contacts and connect the brush shifting motor IE to the supply source 3| through the field winding "5.. The motor "5 shifts the brushes of the kiln driving motor I! in such a direction as to increase its speed and thereby to increase the speed at which the kiln is rotated.

As the speed of the kiln driving motor I2 is increased, the voltage supplied by the pilot generator 39 increases in proportion, and since the polarity of this voltage across the resistance 35 in the grid circuit of the electric valve is opposite to the polarity of the voltage drop across the resistance 33. the grid voltage of the valve 20 is reduced. When the speed of the kiln has increased to a value such that the opposing Volta-"c supplied by the generator 39 overcomes the previous increased voltage drop across the resistance 33 due to the increased current in the photoelectric cell circuit produced by the rise in temperature, the valve. 20 becomes non-conducting and the contactor 22 is deenergized. The contacts of contactor 22 open in response to deenergization thereby disconnecting the pilot motor i6 from the supply source 3| and the kiln driving motor |2 continues to rotate at the increased speed determined by the setting of its brushes. If the temperature increases still further the foregoing operation is repeated until the temperature rise of the kiln is checked.

However. since the motor I2 con inues to drive the kiln at the increased s eed. the kiln t mperaure will finally begin to fall. In the absence of means for opposin the increased volta e drop across the resistance 33 in the gr d c rcu t of the electric valve appara us produc d by th empera ture rise. the electr c valve 2| would rem in energized until the tempera ure had fallen below the predeterm ned value which the control is adjusted to hold. As av result of this. the brush shifting mo or could not be ener zed to decrease the s eed of the kiln motor until the k ln temperature had fallen below this predeterm ned value. In response to he dec easin volta e drop ac oss the res stance 33 in the grid circuit. produced by the falling k ln emperature. the valve 2| would become non-conducting as the kiln temperature fell below the desired predetermin d value. This would deener ze t e contactor 23 and allow its contacts to close and energize the brush shiftin motor Hi to decrease he speed of the ki n motor. There would he a considerable me lag between the chan e in the kiln speed a d the response of the k ln temperature. a a re u t of wh ch time lag. the kiln emperature would continue to fall below the prede ermined value for some time before the fall could be checked bv the decreasin kiln speed. S milarly, after the fall in the kiln temperature had been checked and had begun to rise. the kiln speed could not be increased until the rise had proceeded be o d th predeterm ned valu A ain. the tem eratur would continue to rise some time before it could be checked. Thus. it will be clea-rlv seen. that this tendenc to overshoot or hunt would produce very unstable and even erratic operation together with wide fluctuations in the kiln tem ra ure which would result in serious impairment of the quality of the product.

This undesirable overshooting or huntin' action is substantially eliminated by the in roduction of an op osing voltage in the grid circuit of the electric valve apparatus. When the initial rise of the kiln temperature has been checked by the increased speed of the kiln. the result ng increased voltage of the genera or 39 produces an i creased voltage drop across the resistance 36 in the grid circuit which opposes and balances the increased voltage drop across the resistance 33 produced by the rise in the temperature of the kiln. Thus the actual grid voltage of the valve 2| at this increased kiln temperature is the same as the grid voltage at the normal predetermined kiln temperature. Consequently the valve 2| will become non-conducting in response to a very slight decrease in the kiln temperature. As a result the contactor 23 is deenergized and its contacts close to energize the brush shifting motor 6 to decrease the speed of the kiln driving motor l2. Thus, in effect the generator 39 operates to change the firing point of the electric valves with respect to temperature of the kiln and the correcting action is initiated immediately the temperature begins to fall and without waiting until it has fallen below the predetermined desired value. As a result. the final zone temperature does not fall below the predetermined value and the over-shooting or hunting action is substantially eliminated.

Similarly, if the kiln is operating with the temperature at its predetermined value and a sudden decrease in temperature occurs, the voltage drop across the resistance33 decreases. renderlng the valve 2| non-conducting and allowing the contactor 23 to close its contacts and energize the brush shifting motor Hi to decrease the speed of the kiln. As the speed of the kiln motor decreases, the voltage of the pilot generator 39 decreasesin proportion, thereby decreasing the voltagedrop across the resistance 36 to a point at which the decreased voltage drop across the resistance 33 produced by the decreasing kiln temperature is balanced. Thereupon the valve 2| again becomes conducting and energizes the contactor 23, thereby causing it to deenergize the brush shifting motor IS. The motor |2 continues to drive the kiln l at the decreased speed. If the temperature of the kiln should continue to decrease, this action is repeated until the fall of the kiln temperature is checked. As a result of the decreased speed of the kiln motor l2, the voltage of the generator 39 decreases and the resulting decreased voltage drop across the resistance 36 in the grid circuit opposes and balances the decreased voltage drop across the resistance 33 produced by the decrease in the temperature of the kiln. Thus, the actual grid voltage of the valve 20 at this decreased kiln temperature is same as the grid voltage at the normal predetermined kiln temperature. Consequently, the valve 20 will become conducting in response to a very slight increase in the kiln temperature to start the brush shifting motor IE to increase the speed of the kiln. Since the correcting action is initiated as soon as the temperature begins to rise, the kiln temperature will not rise above the predetermined value and thus overshooting or hunting is substantially prevented.

Although in accordance with the provisions of the patent statutes, this invention is described as embodied in concrete form, it will be understood that the elements and their organization shown and described are merely illustrative and that the invention is not limited thereto, since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

' What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a control system the combination with a device to be controlled, motor means for controlling an operating characteristic of said decomprising means for producing a control volt-- age varying with said characteristic and electric valve apparatus controlled by said voltage for controlling said motor means, means for controlling said valve apparatus to respond at a predetermined value of said control voltage and a pilot generator driven by said motor means for producing a voltage opposing said control voltage thereby to cause said valve apparatus to respend to a difierent value of said control voltage.

2. A control system comprising in combination with a device to be controlled, an electric motor for controlling said device, means for controlling said motor to efiect respectively opposite controlling actions of said device comprising a control circuit, a device for introducing a voltage in said circuit varying with an operating condition of said controlled device, electric valve apparatus connected to said control circuit and responsive to opposite variations of said voltage from a predetermined value for causing said motor to efiect respectively opposite controlling actions on said controlled device and a pilot generator driven by said motor and connected to said circuit for introducing an opposing voltage in said circuit thereby to change the response adjustment of said valve apparatus and to eliminate hunting action.

3. A control system for rotary kilns and the like comprising an electric motor for driving the kiln, means responsive to variations of the temperature of the kiln from a predetermined value for producing a control voltage varying with said temperature and electric valve apparatus responsive to a predetermined value of said control voltage for varying the speed of said motor, and means operatively connected with said motor for supplying a voltage varying with the speed thereof and opposing said control voltage thereby to cause said valve apparatus to respond to a diiierent value of kiln temperature.

4. A control system for rotary kilns and'the like comprising an electric motor for driving the kiln, means responsive to the radiant energy of the kiln for producing a control voltage varying with the temperature of the kiln, electric valve apparatus responsive to a predetermined value of said voltage for varying the speed or" said motor, and a pilot generator driven by said motor for producing a voltage opposing said control voltage thereby to cause said valve apparatus to respond to a difierent value of control voltage.

5. A control system for rotary kilns and the like comprising a motor for driving the kiln, means for controlling the speed of said motor, a device responsive to the radiant energy of the kiln for producing a control voltage varying with the temperature of the kiln, electric valve apparatus responsive to variations of said voltage above and below a predetermined value for actuating said speed varying means to increase and decrease the speed of said motor respectively, and a pilot generator driven by said kiln mo tor for producing a voltage in opposition to said control voltage thereby to cause said valve apparatus to be responsive to a different value of control voltage and kiln temperature so as to eliminate hunting action.

6. A control system for rotary kilns and the like comprising a motor for driving the kiln, means for varying the speed of said motor, means for actuating said speed varying means to increase the speed of said motor comprising an electric valve provided with a control grid, means for actuating said speed varying means to decrease the speed of said motor comprising a second electric valve provided with a control grid, a device responsive to the radiant energy of the kiln for supplying a voltage to said grids varying with the temperature of the kiln whereby said valves are respectively actuated in response to temperature variations above and below a predetermined value, and a pilot generator driven by said motor for supplying an opposing voltage to said grid whereby said valves are caused to respond at a difierent kiln temperature and to eliminate hunting action.

7. A control system for rotary kilns and the like comprising a motor for driving the kiln, means responsive to variations in the temperature of the kiln from a predetermined value for producing a varying control voltage, electric valve apparatus having a control electrode connected to be responsive to said variable control voltage, means controlled by said valve for efiecting variations in the speed of said motor in response to said variations in said control voltage, and means re-' sponsive to the speed of said motor for supplying tosaid control electrode a voltage opposing said control voltage and varying with said speed thereby to cause said valve apparatus-to respond to variations of said temperature from a new value.

8. A control system for kilns and the like comprising a motor for controlling the rate of progess of material through the kiln, means responsive to a variation of the temperature of said material from a predetermined value for changing the speed of said motor to decrease said temperature variation and means for terminating the change of said motor speed before the temperature is restored to said value.

9. A control system for kilns and the like comprising a motor for rotating the kiln to control the progress of the material through the kiln, means actuated by the radiant energy of said material for changing the speed of said motor in response to a variation of the temperature of said material from a predetermined value, thereby to decrease said temperature variation, and means responsive to the change in speed of said motor for terminating the action of said speed changing means before said. temperature is restored to said value.

10. A control system for kilns and the like comprising means for controlling the temperature of the material within said kiln, means responsive to a deviation of the temperature of said material from a predetermined value for actuating said control means to check said deviation, and means for varying said predetermined temperature value of response to a new value in accordance with the amount of said deviation.

11. A control system for kilns and the like, comprising means for controlling the temperature of the material within the kiln, means responsive to a predetermined deviation of the temperature of said material from a predetermined desired value for actuating said control means to check said deviation, and means responsive to actuation of said control means for causing said temperature deviation responsive means to respond to deviations of said tempera ture from a new value.

JAMES R. ALEXANDER, JR. 

